The book JBoss in Action (http://www.manning.com/jamae) contains two chapters in JBoss Portal. The first is a tutorial on developing a portlet using JSPs. (Sorry, but I did not have enough space to cover JSF/Struts/Seam/Wicket/Tapestry/Grails/your-favorite-framework-here). The second chapter goes into portal administration topics, and ends with constructing a custom portal (my JBossWorld presentation was based on this).

Another book, which is older but free, I also found helpful was http://www.manning.com/hepper/. It doesn't use JBoss Portal, but the information on writing porltets is decent.